It is known in the prior art to hydro-form tubing or thin walled containers into a desired external configuration. In the prior art methods the tubing or container is enclosed in a die having an internal configuration that corresponds to the external configuration of the tubing or container to be formed. The inner surface of the die mates with and abuts against the outer surface of the portion of the tubing or the container to be formed thereby securely holding the tubing or container in place. Cavities are located in the inner surface of the container and are located and shaped to correspond to the desired external configuration of the tubing or container. In this way, the inner surface of the die supports the tubing or container where there is to be no forming of the wall(s) of the tubing or container, and the portions of the wall(s) that are to be deformed overlie the cavities and are unsupported by the die.
When pressurized hydraulic fluid is applied to the interior of the tubing or container, the pressurized fluid presses against the interior surface of the wall(s) of the tubing or container and the unsupported portions of the wall(s) are deformed outward into the cavities. Thus the wall(s) are deformed by the pressurized fluid into the desired configuration.
In one prior art method of supplying the pressurized fluid to the interior of the tubing, the ends of the tubing are held in place and sealed fluid tight by holders, one of which has a supply channel therein for supplying hydraulic fluid to the interior of the tubing. This method requires a tight fit between the holders and the tubing necessitating careful insertion of the holders into the die or tubing. A relatively large amount of hydraulic fluid is also required to fill the tubing before the fluid can be pressurized to deform the tubing wall. These two drawbacks considerably slow down the process making it unsuitable for mass production.
Another prior art method attempts to alleviate the need to fill the tubing with fluid of the above prior art method by inserting an hydraulic fluid filled probe or needle that has a fluid supply passage therein into the tubing or container. Holes are arranged in the sides of the needle to supply pressurized fluid directly to the portions of the wall(s) to be deformed when the needle is fully inserted into the tubing. According to this method, O-rings are mounted on the needle adjacent either side of each opening sealing the fluid in the area immediately around the opening and the portion of the tubing to be deformed.
This arrangement eliminates the need to fill the entire tube or container with pressurized fluid. The fluid is supplied directly to the portions of the wall to be deformed and is sealed in a very small space around the portions to be deformed by the 0-rings. Therefore, a pulse of pressurized fluid is sufficient to deform the wall(s) of the tubing or container saving the time required to fill the tubing with fluid greatly speeding up the actual deformation process itself. The prior art is not applicable to miniature tubing with inside diameters of as little as 2 mm or less. If "O" rings are used, the needle must be reduced in cross-section at the "O" ring locations, rendering it very fragile both to insertion stresses and the hydraulically induced stresses during the forming process. Also the "O" rings are vulnerable to rapid wear in production due to variable surface quality of the tubing inside surface and there is the practical problem of finding or making "O" rings in these miniature sizes which will tolerate the forming pressure required. If the needle is forced into the tubing with no "O" rings as an interference fit, the resulting stresses in the needle will in most cases cause the needle to buckle as an overloaded column and break.